Which is better?

[Jiro Dimple]

Windows 7 Pro or Windows 8.1 SL?

And what is the meaning of SL?

 

[laviniuc]

Regional restrictions and variations[edit]
All mentioned editions have the ability to use language packs, enabling multiple user interface languages.[5] (This functionality was previously only available in Windows 7 Ultimate or Enterprise.) However, in China and other emerging markets, a variation of Windows 8 without this capability, called Windows 8 Single Language, is sold. This edition can be upgraded to Windows 8 Pro.[14]

Additional Windows 8 editions specially destined for European markets have the letter "N" (e.g. Windows 8.1 Enterprise N) suffixed to their names and do not include a bundled copy of Windows Media Player. Microsoft was required to create the "N" editions of Windows after the European Commission ruled in 2004 that it needed to provide a copy of Windows without Windows Media Player tied in.

windows 8.1 is the better choice, you can upgrade either one to win10 when it arrives anyway